The present invention relates to a compressor, and more particularly to an endwall treatment disposed in a casing of such compressor to provide a delay in compressor stall.
Compressors used in engines such as a gas turbine, may include a plurality of stages arranged along a length of the compressor. Each stage may include a hub and a plurality of rotor blades arranged about a circumference of the hub. In addition, each stage may further include a plurality of stator blades, disposed alternately to the plurality of rotor blades and arranged about a circumference of a casing of the compressor.
During operation of such gas turbine, the hub of the compressor may be rotated at high speed by a turbine, such that a fluid is continuously induced into the compressor. The fluid is accelerated by the rotating rotor blades and swept rearwards onto the adjacent rows of the stator blades. At each stage, the rotor blade and/or stator blade increases pressure of the fluid. The operating point at which the compressor starts operating in an unstable condition may be referred to as the stall point of the compressor.
Rain, hail and ice-crystal ingestion are known to occur over the entire range of a flight envelope. Cases of in-flight thrust loss events due to engine icing have been reported during cruise conditions at high altitudes (e.g. 10.000 ft.) and especially in sub-tropical regions. When engines operate in icing conditions, ice may accumulate on the low pressure compression system of the engine. More specifically, if such engines are operated within icing conditions at low power for extended periods of time, ice accumulation within the engine may be significant. Accumulated ice in low pressure compression system may shed and enter high pressure compression system and cause compressor instability including compressor surge, partial or total thrust loss, or power roll-backs with little or virtually no warning.
Engine core ice accretion is a complex process involving ice sticking to hot metal surface and acting like a heat sink. Conventional procedures turn on stall mitigation techniques when ice is detected at the compressor exit. More particularly, in an icing condition, a transient bleed valve (TBV) is opened upon ice detection at the compressor exit to eject the ice crystal buildup before it enters the core engine. During such event, the TBV at the compressor exit is opened to bleed air out thus reducing the compressor exit pressure. This results in reduced compressor capability to compress air and hence reduction in overall thrust generated by turbine. The opening of the TBV typically reduces the flow and engine operating line. This results in increased compressor stall margin and delays a stall event resulting in undesirable thrust loss.
Prior attempts to increase the operating range and delay the stall margin in an icing condition have included flow control based techniques such as plasma actuation and suction/blowing near a blade tip. However, such attempts may significantly increase complexity and weight of the compressor. Other attempts include endwall treatments such as circumferential grooves, axial grooves, and the like. Early attempts on such endwall treatments have a substantial impact on design point efficiency with very minimal benefit in delaying the stall margin of the compressor.
Thus, there is a need for a compressor in which during an icing condition thrust loss is avoided and compressor stall is delayed. In addition, there is a need for a method for improving the stall margin of a compressor during an icing condition.